Exhaust gas recirculation system for automobile engines

ABSTRACT

An exhaust gas recirculation system comprising a flow valve device which is responsive to engine operating conditions in terms of atmospheric and exhaust gas temperatures for blocking introduction of exhaust gases into an engine intake manifold when the atmospheric temperature is lower than a predetermined value or when the exhaust gas temperature is higher than a predetermined value. The blocking action of the valve device is controlled by a bistable metal spring device of the buckling type.

United States Patent Konomi et al. 1 July 8, 1975 [5 EXHAUST GAS RECIRCULATION SYSTEM 3,783,847 1/1974 Kolody 123/119 A x 3,800,764 4/1974 Goto et al 123/119 A FOR AUTOMOBILE ENGINES Inventors: Toshiaki Konomi; Hidetaka Nohira,

both of Susono, Japan Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota, Japan Filed: Dec. 14, 1973 Appl. No.: 424,763

Assignee:

Foreign Application Priority Data Jan. 24, 1973 Japan 48-9480 References Cited UNITED STATES PATENTS 3/1972 Nakajima et al............ I231] 19 A X Primary Examiner--Charles .l. Myhre Assistant Examiner-S. .l. Richter Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57 ABSTRACT An exhaust gas recirculation system comprising a flow valve device which is responsive to engine operating conditions in terms of atmospheric and exhaust gas temperatures for blocking introduction of exhaust gases into an engine intake manifold when the atmospheric temperature is lower than a predetermined value or when the exhaust gas temperature is higher than a predetermined value. The blocking action of the valve device is controlled by a bistable metal spring device of the buckling type.

7 Claims, 8 Drawing Figures 1o 27 29 t I 33 PATEI-JTEDJUL 8 i975 3,893, 435 SHEET 1 FIG. I

FIG. 20 FIG. 2b FIG. 2c

\3 FIG. 3

EXHAUST GAS RECIRCULATION SYSTEM FOR AUTOMOBILE ENGINES BACKGROUND OF THE INVENTION The present invention relates to an exhaust gas recirculation system for an automobile engine, and more especially to a system of the above type including an exhaust gas recirculation conduit extending from an exhaust manifold to a carburetor of the automobile engine for providing communication of engine exhaust gases between the manifold and carburetor, a flow control valve device disposed midway of said exhaust gas recirculation conduit for controlling the communication of the exhaust gases, said valve device having an intake vacuum chamber and including a valve element normally biased into a closing position of said valve device and movable in said valve device, when actuated, into an opening position of said valve device, an intake vacuum conduit extending from an intake manifold of the automobile engine to the intake vacuum chamber of said valve device for introducing an intake vacuum into said intake vacuum chamber, and actuating diaphragm means extending in said valve device for defining said intake vacuum chamber and connected to said valve element for actuating the same in response to a vacuum which is introduced from the intake manifold.

Such an exhaust gas recirculation system is known, and, in a proposed flow control valve device for the system, exhaust gas recirculation is stopped when the engine is accelerated to utilize the full output of the engine. Exhaust gas recirculation is performed, however, when the automobile is running at a substantially constant speed or during deceleration.

By effecting such exhaust gas recirculation, combustion temperature in the engine is decreased to reduce nitrogen oxide concentration in engine exhaust gases. However, such known system involves some serious disadvantages. At a low atmospheric temperature, the intake air to be introduced into an intake manifold is so cold that water vapors, if any, in the recirculated exhaust gases may condense in the intake passage to form ice, which will invite serious operational problems. When exhaust gas temperature is very high, on the contrary, some parts and elements of the flow control valve device such as an electromagnetic valve as well as control and sensing elements and organic elements such as a rubber valve seat, may be damaged by the hot exhaust gas in the recirculation conduit.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide an improved exhaust gas recirculation system having means to prohibit exhaust gas recirculation when atmospheric temperature is lower and when exhaust gas temperature is higher than predetermined values, respectively.

According to a feature of the present invention, temperature responsive bistable metal springs are provided, each of which can be buckled to take two positions by thermal expansion thereof. One of the springs is responsive to the atmospheric temperature, whereas the other spring is responsive to the exhaust gas temperature.

The bistable metal spring can be a hemispherical plate spring, to the apex of which is attached a shaft to project or retract by reversing of the curvature in response to a predetermined temperature. When the shaft projects, it engages with the valve element of the flow control valve device to retain the valve element to close the recirculation conduit.

According to another feature of the present invention, another valve means to close or open the intake vacuum conduit is provided. The shaft of the bistable metal spring projects to retain the valve means to close the conduit, so that the valve element in the flow control valve is retained at a closed position due to the absence of a pressure difference.

Thus, by utilizing simple metal spring means, positive retaining of the valve element can be attained to prohibit recirculation. The spring acts both as a temperature sensing means and as an operating force producing means. The operating force is strong enough to retain or operate the valve element.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in conjunction with preferred embodiments, by way of example, and with reference to accompanying drawings, in which:

FIG. I is a diagrammatic side elevation of an exhaust gas recirculation system according to the invention, the flow control valve of which is shown in a sectional view;

FIGS. 2a, 2b and 20 show the steps of reversing the temperature responsive bistable spring shown in FIG. 1;

FIGS. 3 and 4 are longitudinal sectional views of other embodiments of the flow control valve; and

FIGS. 5 and 6 are longitudinal sectional views of further embodiments, according to the invention, which are applied to open or close an intake vacuum conduit leading to the flow control valve device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. I shows an exhaust gas recirculation system having a flow control valve device 10, according to the present invention, for an engine having an air cleaner 1, a carburetor 2, an intake manifold 3, an engine body 4, an exhaust manifold 5 and an exhaust pipe 6.

The flow control valve device 10 is disposed midway of the exhaust gas recirculation conduits 7 and 8 which are respectively connected with the exhaust manifold S and the carburetor 2. A conduit 9 is connected between the intake manifold 3 and the control valve device 10.

The flow control valve device I0 includes a body 11 having an inlet I2 connected with the conduit 7, an outlet 13 connected with the conduit 8, and a passage 14 connecting the inlet 12 and the outlet 13. A valve element 17 is slidably accommodated in the valve body II and includes an elastic contact member 16 made of rubber to engage with a valve seat 15 which is formed to close the passage 14. A plate I8 secured to the lower end of the valve element I7 is connected with a diaphragm 19, which separates the lower portion of the valve body II both into an upper atmospheric pressure chamber 21 isolated by a bush 20 from the passage I4 and into a lower vacuum chamber 24 connected by an inlet 23 with the conduit 9. A lower casing 22 is connected with the valve body 11, between which the diaphragm 19 is inserted to define the chamber 24. Between the plate 18 and the casing 22, a spring 25 is inserted to urge the valve element 17 into engagement with the valve seat 15, when the vacuum introduced into the chamber 24 is not sufficiently high.

The flow control valve device above described is conventional, and a more detailed description will be omitted here. During acceleration the intake manifold vacuum is not high, the valve element 17 is held at the closing position as shown in FIG. 1 to close off the passage 14. Thus, the exhaust recirculation conduits 7 and 8 are closed off and nitrogen oxide concentration in the exhaust gases is not reduced. During constant-speed running and during deceleration, as the intake manifold vacuum is sufficiently high, the pressure difference between the chambers 21 and 24 is accordingly high, so that the diaphragm 19 is warped downward against the biasing action of the spring 25 to lower the valve element 17 to thereby open the passage 14. A portion of the exhaust gases in the exhaust manifold is then passed through the conduit 7, inlet 12, passage 14, outlet 13 and conduit 8 to the carburetor to thereby recirculate the exhaust gases into the combustion chamber of the engine. Thus, the combustion temperature is decreased to reduce the nitrogen oxide concentration in the exhaust gases.

In the above described conventional flow control valve, a recess 26 is formed in the valve body 11 facing the passage 14. In the recess 26, a high temperature responsive bistable hemispherical metal spring 27 which operates, by thermal expansion, at high limit temperature is retained by a ring 28 with its apex facing rear ward, according to the present invention. At the apex of the metal spring 27, a shaft 29 is secured thereto for engagement with the valve element 17.

Another recess 30 is also formed in the valve body 11 with its concave side facing the outside of the body 11. In the recess 30, a low temperature responsive bistable hemispherical metal spring 31 is retained by a ring 32 with its apex facing outward. At the apex of the spring 31, a shaft 33 is secured thereto for projection into the passage 14 and is engageable with the valve element 17. The metal spring 31 can be buckled at a predetermined value of the atmospheric temperature.

FIG. 2 shows the operating principle of the hemispherical metal springs 27 and 31. FIG. 2a shows the spring 27 at a low temperature. The spring 27 has its concave side facing the opening of the recess 26. When the temperature in the passage 14, i.e., the exhaust gas temperature is increased, the metal spring 27 thermally expands and the apex is urged to the end wall of the recess 26 to flatten the apex as shown in FIG. 2b. As the temperature is further increased above a predetermined value, the apex buckles or is reversely curved by further thermal expansion to instantly reverse the curvature of the metal spring 27 into the second stable position as shown in FIG. 2c. Thus, the shaft 29 is made to project so that the valve element 17 is retained to close the passage 14. As the temperature of exhaust gas in the passage 14 decreases under the predetermined value, the metal spring 27 buckles or contracts to instantly reverse the curvature thereof into the first stable position as shown in FIG. 2a, so that the shaft 29 retracts from the valve element 17.

The hemispherical bistable metal springs 27 and 31 can be made ofa suitable metal or bimetal springs, the heat expansion coefficients of which are different from each other and are bonded to each other to obtain bistable positions by such reverse motion as described above.

When the atmospheric temperature is low, the metal spring 31 is in the first stable position as shown in FIG. 1 to project the shaft 33 toward the passage 14 to retain the valve element 17 at the upper position to thereby close the passage 14 notwithstanding the intake vacuum in the chamber 24 is sufficiently high. As the atmospheric temperature increases to exceed the predetermined value of the spring 31, the spring is reversed to a second stable position as shown in FIG. 20 to thereby retract the shaft 33 from the valve element 17. Thus, the valve element 17 can be moved to open or close the passage 14 in response to intake vacuum in the chamber 24.

Thus, the valve element 17 can be moved in response to the intake vacuum, only in the case where the exhaust gas temperature is lower than the predetermined value and where the atmospheric temperature is higher than the predetermined value.

The flow control valve device 10' as shown in FIG. 3 includes a housing 34, which is secured to the casing 22 to form the intake vacuum chamber 24. In the housing 34, a low temperature responsive hemispherical bistable metal spring 31 having the shaft 33 is provided to have its apex facing the chamber 24 at a first stable position. In the first stable position, the shaft 33 is made to project in the chamber 24 to urge the lower end of the valve element 17 toward an upper position to close the passage 14. One or more openings 35 are formed in the housing 34 to provide communication of the inside of the housing 34 with the atmospheric air.

In the lower side of the housing 34, a high temperature responsive bistable metal spring 27 is provided to have its apex face the lower end of the housing 34 at a first stable position of the spring 27. The spring force of the spring 27 is higher than that of the spring 31, so that a short shaft 29' of the spring 27 urges the spring 31 to the first position, as shown in FIG. 3, whether the spring 31 is initially at the first or second position, when the spring 27 is buckled into the second position. At the lower side of the housing 34, one or more openings 36 are formed to admit the exhaust gases in the conduit 7 which has communication with the inside of the passage 14.

In operation, when the atmospheric temperature is lower than a predetermined value of the spring 31, the spring 31 is held at a first stable position as shown in FIG. 3, so that the shaft 33 is made to project to retain the valve element 17 to thereby close the passage 14. As the atmospheric temperature is increased above the predetermined value, the spring 3] buckles into a second stable position to thereby take the shaft 33 from the valve element 17.

When the exhaust temperature in the conduit 7 is lower than a predetermined value of the spring 27, the spring 27 is kept at the first stable position as shown in FIG. 3. However, when exhaust temperature in the conduit 7 is higher than the predetermined value, the spring 27 buckles into a second stable position to make the short shaft 29' project in the direction of the spring 3LAs the spring force of the spring 27 is higher than that of the spring 31, the short shaft 29' forces the spring 31 to the first stable position to allow the shaft 33 to project, so that the valve element 17 is retained at the closing position. Thus, the valve element 17 closes off the passage 14 to prevent the exhaust recirculation.

The flow control valve device as shown in FIG. 4 also has a similar fundamental construction to that shown in FIG. 1 and has similar elements as shown at the same reference numerals. In the device 10", the

valve body 11 forms a recess 30' which is vented to the atmosphere. The recess 30' is divided by a separator 38 into two spaces. The upper space communicates by openings 37 with the exhaust gases in the passage 14 and accommodates therein the high temperature responsive bistable metal spring 27, which has its apex secured to a shaft 29 and which projects into the passage 14 to retain the valve element 17 at the second stable position corresponding to the high exhaust gas temperature condition in the passage 14. The lower space of the recess 30' accommodates therein the low temperature responsive bistable metal spring 31 which has its apex secured to a shaft 33. This shaft 33 will abut on the shaft 29 to engage the valve with element 17 when the atmospheric temperature is lower than the predetermined value as before. The shaft 33 may be such a short shaft as to force the metal spring 27 into a second stable position. In this case, the spring force of the spring 31 is substantially stronger than that of the spring 27. The operation of the flow control valve device 10" is similar to the flow control valves 10 and 10' as shown in FIGS. 1 and 3.

In the embodiments shown in FIGS. 5 and 6, another flow control valve device 10 is provided midway of the intake vacuum conduit 9, as shown, but includes no means to retain the valve element 17 against the suction of the intake vacuum. Since the valve element 17 is maintained at a closing position when the vacuum in the chamber 24 is not high compared with atmospheric pressure in the chamber 21, means are provided to shut off the conduit 9 to block introduction of the intake vacuum into the chamber 24.

More specifically, as shown in FIG. 5, the conduit 9 includes a valve seat 39, an opening 40 which communicates with the atmosphere at a downstream of the valve seat 39, and a valve element 41 which selectively opens and closes the valve seat 39 and the opening 40. A housing 34' is secured to the exhaust gas recirculation conduit 7. In the housing 34' adjacent the conduit 7, the high temperature responsive bistable metal spring 27 is accommodated and the apex of the spring 27 is adjacent the conduit 7 at a first stable position corresponding to an exhaust gas temperature condition, in which the temperature is lower than a predetermined value of the spring 27. This spring 27 will make a short shaft 29 project from the apex to the valve element 41. The housing 34' is formed with one or more openings 36 to expose the exhaust gas pressure in the conduit 7 to the upper surface of the spring 27.

In the lower portion of the housing 34', a low temperature responsive bistable metal spring 31 is accommodated. The apex of the spring 31 is secured to the valve element 41. At a lower surface of the housing 34', one or more openings 35 are formed to expose the atmospheric pressure to the lower surface of the spring 31. The spring force of the spring 27 is substantially stronger than that of the spring 31, so that the spring 31 may yield to make the valve element 41 project to close the conduit 9 when the spring 27 buckles or reverses into a second stable position.

In operation, when the atmospheric temperature is lower than the predetermined value of the spring 31 or when the exhaust gas temperature in the conduit 7 is higher than the predetermined value of the spring 27, the valve element 41 projects to engage with the valve seal 39 to thereby open the opening 40. Thus, the intake manifold vacuum in the conduit 9 is shut off and only the atmospheric pressure is introduced into the chamber 24 through the opening 40. As a result. the valve element 41 is retained at the closing position to close the passage 14 to thereby prevent the exhaust gas recirculation.

When, on the contrary, the exhaust gas temperature is lower than the predetermined value of the spring 27 and when the atmospheric temperature is higher than the predetermined value of the spring 31, the valve element 41 is retracted to open the conduit 9 and to shut off the opening 40. In this way, the diaphragm I9 responds to the intake manifold vacuum in the conduit 9 and in the chamber 24, so that, when the intake manifold vacuum is sufficiently high, the valve element 17 retracts to open the passage 14 to thereby perform the exhaust gas recirculation through the conduit 7.

In another embodiment as shown in FIG. 6, there are provided in the intake manifold vacuum conduit 9, a valve seat operative to open or close the conduit 9, an opening 43 to provide communication with the atmosphere, a valve element 44 selectively opening one of the valve seat 42 and the opening 43, a cylindrical member or housing 45 secured to the conduit 9 for communication, and a low temperature responsive bistable metal spring 31 which may be retained by a ring 32 in such a manner as described before to have its apex adjacent the wall of the housing 45 facing the conduit 9 at a first stable position. The cylindrical housing 45 provides a plurality of fins so that the housing temperature may become substantially at the same level as that of the atmospheric temperature. The valve element 44 is secured to the apex of the metal spring 31 by means of nuts 46 which can adjust the predetermined temperature value of the spring 31.

Another valve set is inserted in the conduit 9 and includes a valve seat 42 operative to open and close the conduit 9, an opening 43' to provide communication with the atmosphere, a valve element 44' to selectively open one of the valve seat 42 and the opening 43', a cylindrical member or housing 45' connected between the exhaust conduit 7 and the conduit 9, and a high temperature responsive bistable metal spring 27 retained in the housing 45 by means of ring 28 to have its apex facing the exhaust conduit 7 in a first stable position. One or more openings 47 are also formed to transfer the exhaust gas temperature to the spring 27. The valve element 44 is secured to the apex of the metal spring 27. The end of the valve element 44' may preferably be attached to a bolt 48, which can adjust the predetermined temperature value of the spring 27.

When the atmospheric temperature is below the predetermined value of the temperature of the spring 31, the valve element 44 is urged onto the valve seat 42 to close the conduit 9 and to open the opening 43. Thus, the pressure in the chamber 24 of the control valve device 10 is reduced to the atmospheric pressure, so that the valve element 17 is held at the closing position to close the passage 14. When, on the contrary, the atmospheric temperature is increased to the predetermined temperature value of the spring 31, the spring 31 buckles or reverses into the second stable position to open the conduit 9 and to close the opening 43. Thus, conduit 9 transmits the intake manifold vacuum to the chamber 24.

When the exhaust gas temperature is at a normal level, the spring 27 is held at the first stable position, as shown in FIG. 6, to open the conduit 9 and to close the opening 43'. When, in this way, the valve element 44 also opens the conduit 9, the intake manifold vac uum is transmitted into the chamber 24 to control the valve element 17 to thereby open or close the passage 14.

When the exhaust gas temperature in the conduit 7 is increased to exceed the predetermined value of the spring 27, the spring 27 buckles or reverses into the second stable position to urge the valve element 44' onto the valve seat 42' to thereby close the conduit 9 and to thereby open the opening 43'. Then, the atmospheric pressure is transmitted into the chamber 24 to urge the valve element 17 to its closing position, thereby preventing the exhaust recirculation.

The temperature responsive bistable metal springs 27 and 31 are, respectively, hemispherical single metal springs, as described in conjunction with the embodiments. However, suitable plate springs other than a spherical surface, may be used with retainer ring 28 or 32, if they have bistable characteristics. Also, suitable bimetal springs, which are made of two plates having different thermal expansion coefficient and which are secured face to face to each other, may be used, if they provide bistable characteristics by a thermal expansion difference. The spring 27 should be made of corrosionresistant metal such as stainless steel. Such movable element in the exhaust gas conduit 9 or passage 14 as the valve element 17 and the shaft 29 should also be made of heat-resistant and corrosion-resistant material. Such movable element which moves across different temper ature spaces as the shaft 33 and the valve element 41 and 43 should be made of heat-insulating material.

It will be appreciated that, according to the present invention, the valve element 17 of the conventional flow control device is retained to a closing position when the atmospheric temperature is low or when the exhaust gas temperature is too high, to thereby stop exhaust gas recirculation. Thus, the foregoing disadvantages are eliminated.

By utilizing such temperature responsive bistable metal springs 27 and 31 as may buckle or reverse into the second stable position by thermal expansion, the retaining operation is very simple, and long life, simplified maintenance, positive and strong force, and elongated displacement can be attained.

What is claimed is:

1. In an exhaust gas recirculation system for an automobile engine, comprising an exhaust gas recirculation conduit extending from an exhaust manifold to an intake system of the automobile engine for providing communication of engine exhaust gases between the manifold and carburetor, a flow control valve device disposed midway of said exhaust gas recirculation conduit for controlling the communication of the exhaust gases, said valve device having an intake vacuum chamber and including a valve element normally biased into a closing position of said valve device and movable in said valve device, when actuated, into an opening position of said valve device, an intake vacuum conduit extending from an intake manifold of the automobile engine to the intake vacuum chamber of said valve device for introducing an intake vacuum into said intake vacuum chamber, and actuating diaphragm means extend ing in said valve device for defining said intake vacuum chamber and connected to said valve element for actuating the same in response to a vacuum which is introduced from the intake manifold, the improvement comprising means including temperature responsive bistable metal spring means, responsive to the operating conditions of the automobile engine in terms of temperatures of both the atmospheric air and the exhaust gases both, for leaving the actuating action of said diaphragm means free only in the case where the temperature of the atmospheric air is higher than a first predetermined value and where the temperature of the exhaust gases is lower than a second predetermined value and for buckling in the remaining operating conditions of the automobile engine to render the actuating action of said diaphragm means inoperative so that said valve element may be held in the closing position even in the presence of the vacuum in the intake vacuum chamber of said valve device.

2. An improved exhaust gas recirculation system according to claim 1, wherein said metal spring means includes a lower metal spring element responsive to the temperature of the atmospheric air for buckling at the first predetermined value, a higher metal spring element responsive to the temperature of the exhaust gases for buckling at the second predetermined value, a lower shaft secured to the apex of said lower metal spring element for projecting and retracting in response to the buckling action of the same, and a higher shaft secured to the apex of said higher metal spring element for projecting and retracting in response to the buckling action of the same, at least either of the lower and higher shaft being, when projecting, engageable directly with said valve element for retaining the same in the closing position.

3. An improved exhaust gas recirculation system according to claim 2, wherein both of said lower and higher shafts are engageable with said valve element independently of each other.

4. An improved exhaust gas recirculation system according to claim 2, wherein the lower and higher metal spring elements are arranged to overlie each other in a manner in which said lower and higher shafts are aligned with each other and in which the lower shaft abuts the higher shaft, and wherein said lower metal spring element has a stronger spring force than said higher metal spring element and the higher shaft is engageable directly with said valve element.

5. An improved exhaust gas recirculation system according to claim 1, wherein said metal spring means includes a lower metal spring element responsive to the temperature of the atmospheric air for buckling at the first predetermined value, a higher metal spring element overlying and in alignment with said lower metal spring element and being responsive to the temperature of the exhaust gases for buckling at the second predetermined value, a common shaft secured both to the apex of said lower metal spring element and to said valve element, and wherein said higher metal spring element has a stronger spring force than said lower metal spring element.

6. An improved exhaust gas recirculation system according to claim 1, wherein said means responsive to the operating conditions of the automobile engine includes valve means disposed midway of said intake vacuum conduit for controlling the intake vacuum into the either of the apices of the lower and higher metal spring elements and to said at least one valve element of said valve means for actuating the same into either of the first and second positions.

7. An improved exhaust gas recirculation system according to claim 6, wherein said metal spring means includes two adjusting screws attached to said at least one shaft for adjusting the spring forces of said lower and higher metal spring elements. 

1. In an exhaust gas recirculation system for an automobile engine, comprising an exhaust gas recirculation conduit extending from an exhaust manifold to an intake system of the automobile engine for providing communication of engine exhaust gases between the manifold and carburetor, a flow control valve device disposed midway of said exhaust gas recirculation conduit for controlling the communication of the exhaust gases, said valve device having an intake vacuum chamber and including a valve element normally biased into a closing position of said valve device and movable in said valve device, when actuated, into an opening position of said valve device, an intake vacuum conduit extending from an intake manifold of the automobile engine to the intake vacuum chamber of said valve device for introducing an intake vacuum into said intake vacuum chamber, and actuating diaphragm means extending in said valve device for defining said intake vacuum chamber and connected to said valve element for actuating the same in response to a vacuum which is introduced from the intake manifold, the improvement comprising means including temperature responsive bistable metal spring means, responsive to the operating conditions of the automobile engine in terms of temperatures of both the atmospheric air and the exhaust gases both, for leaving the actuating action of said diaphragm means free only in the case where the temperature of the atmospheric air is higher than a first predetermined value and where the temperature of the exhaust gases is lower than a second predetermined value and for buckling in the remaining operating conditions of the automobile engine to render the actuating action of said diaphragm means inoperative so that said valve element may be held in the closing position even in the presence of the vacuum in the intake vacuum chamber of said valve device.
 2. An improved exhaust gas recirculation system according to claim 1, wherein said metal spring means includes a lower metal spring element responsive to the temperature of the atmospheric air for buckling at the first predetermined value, a higher metal spring element responsive to the temperature of the exhaust gases for buckling at the second predetermined value, a lower shaft secured to the apex of said lower metal spring element for projecting and retracting in response to the buckling action of the same, and a higher shaft secured to the apex of said higher metal spring element for projecting and retracting in response to the buckling action of the same, at least either of the lower and higher shaft being, when projecting, engageable directly with said valve element for retaining the same in the closing position.
 3. An improved exhaust gas recirculation system according to claim 2, wherein both of said lower and higher shafts are engageable with said valve element independently of each other.
 4. An improved exhaust gas recirculation system according to claim 2, wherein the lower and higher metal spring elements are arranged to overlie each other in a manner in which said lower and higher shafts are aligned with each other and in which the lower shaft abuts the higher shaft, and wherein said lower metal spring element has a stronger spring force than said higher metal spring element and the higher shaft is engageable directly with said valve element.
 5. An improved exhaust gas recirculation system according to claim 1, wherein said metal spring means includes a lower metal spring element responsive to the temperature of the atmospheric air for buckling at the first predetermined value, a higher metal spring element overlying and in alignment with said lower metal spring element and being responsive to the temperature of the exhaust gases for buckling at the second predetermined value, a common shaft secured both to the apex of said lower metal spring element and to said valve element, and wherein said higher metal spring element has a stronger spring force than said lower metal spring element.
 6. An improved exhaust gas recirculation system according to claim 1, wherein said means responsive to the operating conditions of the automobile engine includes valve means disposed midway of said intake vacuum conduit for controlling the intake vacuum into the intake vacuum chamber of said valve device and including at least one valve element movable into a first position to allow the introduction of the vacuum into said intake vacuum chamber and into a second position to block said introduction, and wherein said metal spring means includes a lower metal spring element responsive to the temperature of the atmospheric air for buckling at the first predetermined value, a higher metal spring element responsive to the temperature of the exhaust gases for buckling at the second predetermined value, and at least one shaft secured to at least either of the apices of the lower and higher metal spring elements and to said at least one valve element of said valve means for actuating the same into either of the first and second positions.
 7. An improved exhaust gas recirculation system according to claim 6, wherein said metal spring means includes two adjusting screws attached to said at least one shaft for adjusting the spring forces of said lower and higher metal spring elements. 